Si Particles Research Articles

Integrating with a tough framework and efficient self-healing behavior based on a flexible polymer skeleton for Si anode binders in lithium-ion cells

As a prospective and efficient strategy to address the volume expansion of the Si nanoparticles, the binder plays an increasingly significant role in the Si anode of lithium-ion batteries. Based on the inspiration of natural physics and cross-linked networks, a functional (named polyacrylic acid-citric acid-polyethyleneimine) binder that is similar to a flexible polymer skeleton integrated with a tough framework and efficient self-healing behavior is designed to achieve long cycling stability for Si anodes. The cross-linked network can be stabilized by the amide bonds, formed by polyethyleneimine (PEI) and polyacrylic acid (PAA). Based on this, citric acid (CA) can be added to form multiple hydrogen bonds, whose carboxyl groups can also establish a more reversible cross-linked network with Si particles. Then, PEI and CA molecules can connect with PAA to form a “rigid and flexible” structure. The expansion stress of Si nanoparticles is relieved by the protective buffer layer built by the addition of PEI and CA molecules. In addition, PAA, PEI, and CA work together to solve the problem that the action of CA and PAA alone cannot perform well under large currents. Hence, this water-based binder with a three-dimensional cross-linked network structure with self-healing ability has better performance during cycling: at a current density of 0.2C, it still has a capacity of 2017.4 mAh·g−1 after 200 cycles, with a capacity retention rate of 80.7 % (1745.3 mAh·g−1, 300 cycles, a capacity retention of 74.9 %).

Effect of initial heat treatment of A390 alloy on microstructure and tribological behavior of friction surfaced coating

In this study, the effect of the A390 alloy consumable rod's three preprocessing heat treatment conditions (homogenization, solid solution, and artificial aging treatment) on the microstructural evolution, mechanical properties, and wear resistance of the friction surfaced coating applied on a commercially pure aluminum alloy substrate was investigated. The results showed that friction surfacing using artificially aged and solid solution-treated consumable rods results in minimum (3.45 ± 0.35 μm) and maximum (5.63 ± 0.25 μm) coating grain sizes, respectively. Friction surfacing using artificially aged treated consumable rods results in smaller, more uniformly distributed Si particles in the coating microstructure. The [111] and [101] directions of most grains in the consumable rod and coating are parallel to the consumable rod axial axis and surfacing direction, respectively. Recrystallization texture components, including Goss and Cube-Twin, are observed in coatings. Compared to the other consumable rods, the coatings fabricated using artificially aged treated consumable rod result in highest hardness (117.62 ± 9.58 HV0.1), maximum bond strength (13.98 ± 1.02 kN), and lowest wear rate (5.6 ± 0.8 μg/m).

Investigation of the interface precipitation on α-Al(Fe,Mn)Si particles in Al–Fe–Mn–Si–Mg–Cu alloy

The effects of particles on precipitation reactions in aluminum alloy have been widely unknown. Al–Fe–Mn–Si–Mg–Cu alloy strengthened with uniformly distributed Al(Fe,Mn)Si nanoparticles was successfully produced in this study. The alloy was then characterised using high-resolution scanning transmission electron microscopy (HRTEM), to provide a fundamental insight into the interface precipitation. Interfacial precipitations of several tens of nanometers in size was formed after aging, which were found to be Al5Cu6Mg2 and Si phases. The results demonstrated that the facetted α-Al(Fe,Mn)Si particles had a significant influence on precipitation adjacent to the α-Al(Fe,Mn)Si/Al interfaces. Semi-coherent α-Al(Fe,Mn)Si/Al interfaces were revealed to have periodically spaced misfit dislocations that are generally considered to be beneficial to heterogeneous precipitation. They not only reduce nucleation energy barriers but also act as short-circuit diffusion paths to accelerate growth rates by transporting solute atoms and vacancies.

Stable "snow lantern-like" aggregates of silicon nanoparticles suitable as a drug delivery platform.

Nanomedicine is a growing field where development of novel organic and inorganic materials is essential to meet the complex requirements for drug delivery. This includes biocompatibility, suitability for surface modifications, biodegradability, and stability sufficient to carry a drug payload through various tissues for the desired timespan. Porous silicon nanoparticles (pSi NP) are shown to have several beneficial traits in drug delivery in addition to a porous structure to maximize drug loading. The conventional synthesis of pSi NP using electrochemical etching is costly, time-consuming and requires large quantities of highly toxic hydrofluoric acid (HF). As such this research attempted a novel method to address these limitations. Mesoporous silicon nanoparticles were prepared by centrifugal Chemical Vapor Deposition (cCVD) without the use of HF. This process generated aggregates consisting of multiple primary particles fused into each other, similar to snowballs fused together in a snow-lantern (snowball pyramid). Our results demonstrated that the cCVD Si particles were versatile in terms of surface chemistry, colloidal stability, degradability, minimization of acute in vitro toxicity, and modulation of drug release. Dynamic light scattering, scanning electron microscopy, and cryogenic nitrogen adsorption isotherm measurements confirmed the overall size (210 nm), morphology, and pore size (14-16 nm) of the prepared materials. Agglomeration in phosphate-buffered saline (PBS) was minimized by PEGylation by a two-step grafting procedure that employed a primary amine linker. Finally, the release rate of a model drug, hydrocortisone, was evaluated with both PEGylated and pristine particles. Conclusively, these snow-lantern cCVD Si particles do indeed appear suitable for drug delivery.

Effect of preprocessing heat treatment of the Al-16Si-4Cu alloy on microstructure and tribological behavior of friction-surfaced coating

This study investigated the simultaneous effect of the consumable rod's preprocessing heat treatment conditions (homogenization, solid solution, and artificial aging treatment) and severe plastic deformation on the properties of Al-Si-Cu alloy friction surfaced on a commercially pure aluminum alloy substrate. The friction-surfaced coating's microstructural evolution, mechanical properties, and wear resistance were evaluated. The results showed that coatings fabricated using artificially aging (T6)-treated consumable rods resulted in the highest coating width (17.02±0.83 mm) and maximum efficiency (39.78 ± 1.23 %). Friction surfacing using artificially aged and solid solution-treated consumable rods results in minimum (2.78 ± 0.28 µm) and maximum (6.32±0.34 µm) coating grain sizes, respectively. Friction surfacing using T6-treated consumable rods results in smaller, more uniformly distributed Si particles in the coating microstructure. Compared to the other consumable rods, the coatings fabricated using T6-treated consumable rods result in the highest hardness (110.54±10.29 HV0.1), maximum bond strength (14.15±0.75 kN), and lowest wear rate (0.20±0.03 µg/Nm).

Development of Dual-Functional Polyamide Imidazole Binder for Silicon Anode Lithium-Ion Battery

Silicon (Si) is one of the most promising anode materials in lithium-ion batteries (LIBs). However, Si undergoes a huge volume change during charging/discharging and induces intractable problems such as delamination, cracking of electrode, and unstable solid electrolyte interphase. Polymer binder is one of powerful strategies to prevent the problem. In this study, the novel polyamide imidazole (PAID) binder is synthesized and forms imide and imidazole intermediate phase (i-PAID) at electrode fabrication temperature. The i-PAID binder have strong interaction with Si particle and carbon black by ambidextrous binding effect. Introduction of amine and carboxylic acid in i-PAID binder enhances adhesion force of the Si particles. In addition, the extended polymer backbone of i-PAID improves not only inter-molecular interaction with carbon black by π-π stacking interaction but also sustains robust conduction pathway in Si anode. The Si anode with i-PAID binder confirmed outstanding mechanical durability of Si during charging/discharging through in-situ electrochemical dilatometer and ex-situ SEM observation. It exhibited higher reversible capacity and stable cycle performance for 200 cycles at 0.2C than the Si anode with commercial polyimide binder, respectively. Thus, the ambidextrous polymer binder would propose new molecular design concept for Si anode in LIBs.

Studying Degradation of Micro- and Nano-Scale Silicon in Si/ Rgo-Anode Materials for Lithium-Ion Batteries – Towards a Fair Comparison

An attractive approach to increase the Li+-storage capacity of anode materials in Lithium-ion batteries (LiBs), is to replace or combine the routinely-applied graphite (372 mAh g-1) with higher-capacity materials. Among others, silicon (Si) with a theoretical capacity of 3579 mAh g-1 is a promising candidate [1]. Silicon is not yet been used as an anode material in its pure form, due to its low conductivity and volume increase of up to 300 % during lithiation. This two-step expansion (1st: Si + 2 Li+ + 2 e- → SiLi2.0; 2nd: SiLi2.0 + 1.5 Li+ + 1.5 e- → SiLi3.5) is a source of mechanical stress that can ultimately lead to battery failure. Furthermore, the initial lithiation of crystalline silicon (c-Si + 3.5 Li+ + 3.5 e- → SiLi3.5) causes an amorphization of the pristine crystalline lattice. This structural change causes further degradation of the material, which can hardly be avoided [2].The main degradation mechanisms resulting from expansion and amorphization are I) The uncontrolled formation of a passivation layer due to the cyclic volume change taking place during (de-)lithiation, which leads to a continuous break-up and reformation of the solid electrolyte interphase (SEI). II) The pulverization of particles resulting in mechanical stress and the electrical isolation of particles or particle fragments delaminating from the electrode [3]. The first mechanism discussed is more dominant for nanometer scaled particles (nm-Si), while the second mechanism occurs mostly for particles in the micrometer range (µm-Si).Our approach combines, nm- or µm-sized Si particles with different matrix materials. By incorporating the particles into an either graphitic or soft carbon-like support, we aim to increase the conductivity of the electrode material and gain additional buffer space thereby reducing interparticle mechanical stress [4]. On the one hand, the systems of carbon-based anode materials are already well understood in terms of electrode composition, processing parameters, electrolyte compatibility, formation of a stable SEI and the resulting high cycling stability. On the other hand, the observed degradation mechanisms will occur with different predominance in different Si/C composites depending on the Si particle size and the chosen carbon matrix. However, the latter is not completely understood. We will address these issues by comparing different Si/C-composites consisting of nm-Si-particles or µm-Si particles in a reduced graphite oxide (rGO) matrix and in a graphite-matrix.Electrochemical methods, such as galvanostatic cycling, impedance spectroscopy and dq/dU-analysis in 2- and 3-electrode setups, were coupled with optical and spectroscopical techniques (e.g. XRD, FTIR, SEM) to trace back the electrochemically measurable degradation of the electrode to structural changes during formation and cycling. Particular attention was paid to the localization and analysis of defect areas with increased degradation by correlating the optical and spectroscopical results data with the lithiation and delithiation processes. Considering the different SoC levels, we can identify the ongoing aging of the different electrode materials. Based on this, we propose the use of soft carbon-like structures such as rGO as a matrix material for Si/C composites due to its higher cycling stability under the investigated conditions.

Investigating the Use of Mg-3Pb Alloy for Cathodic Protection of Mg Alloys

Magnesium alloys possess many interesting properties, including high strength-to-weight ratios, good castability, and excellent biocompatibility. However, its use has been limited because they are also highly reactive and susceptible to corrosion in aqueous environments. As a result, the development of effective corrosion protection strategies for Mg alloys represents a significant challenge for many industrial applications, particularly in the aerospace, automotive, and biomedical industries.Sacrificial cathodic protection is a commonly used strategy to enhance the durability of metallic materials. This method involves the use of an active metal (known as the sacrificial anode) in galvanic contact with the metal to be protected from corrosion, which acts as the cathode. Due to their low corrosion potential, Mg alloys have traditionally served as sacrificial anodes to protect more noble metals such as steel, aluminum, and zinc. However, the growing interest in Mg alloys for industrial applications has led to the development of effective corrosion protection alternatives for Mg alloy components. Among them, the use of Mg alloy coatings as the anode material for the sacrificial protection of other Mg alloys is an interesting strategy. This approach offers several advantages such as minimized galvanic corrosion due to their comparable electrochemical behavior, as well as enhanced adhesion between the anode and the substrate.One of the key requirements for a metallic material to be used as a sacrificial anode is that its electrode potential must be more negative than that of the metal being protected. Additionally, the anode material must be chemically stable in the environment in which it will be located. These conditions are largely dependent on the composition of the anode material. Although recent studies have aimed to enhance the cathodic protection properties of Mg alloys for their use in industrial applications, such work remains restricted. This is due to the limited number of alloying elements with lower standard reduction potentials than Mg that are stable in solution, thereby decreasing the anode corrosion potential. In addition, Mg exhibits enhanced hydrogen evolution rates with increasing anodic polarization, which contradicts expectations of standard electrochemical kinetics and leads to significantly increased rates of self-dissolution. This phenomenon is termed anomalous hydrogen evolution (HE).This work investigates the potential of Mg-3Pb alloy as possible sacrificial anode material for the corrosion protection of three industrially important Mg alloys: AZ31, AM60, and AZ91. For that purpose, a Mg-3Pb alloy was casted in-house and its microstructural characteristics and electrochemical behavior were studied. Furthermore, galvanic corrosion between the Mg-3Pb alloy and the industrially relevant Mg alloys, AZ31, AM60, and AZ91, was evaluated in 0.1 M NaCl solution. The choice of Pb as an alloying element was motivated by its extremely low exchange current density for the HE reaction (i0,H2,Pb) on the order of 10-12 A/cm2. This was expected to result in reduced HE rates under cathodic polarization, which shifts the corrosion potential (Ecorr) to more negative values, and during anodic polarization, hindering anomalous HE and reducing self-dissolution.The microstructural characterization of the Mg-3Pb alloy revealed that it consisted of large α-Mg grains with the presence of a small amount of secondary phases, including Al, Si, Mn, Fe-containing intermetallics and oxide particles. Additionally, scanning electron microscopy revealed the occurrence of remarkable Pb segregation at grain boundaries.Electrochemical measurements showed that the Ecorr associated with the Mg-3Pb alloy was consistently lower than those of the AZ31, AM60, and AZ91 alloys during 24 hours of immersion in the test solution. Moreover, potentiodynamic polarization confirmed that the Mg-3Pb alloy exhibited the lowest cathodic kinetics. In terms of anomalous HE, which is directly related to the self-dissolution rate of the Mg alloy anode material, galvanostatic polarization at different anodic current densities showed that the HE current densities were linear with respect to the applied current density. Additionally, the charge associated with the HE was in the range of 40–50% of the applied anodic charge, which is consistent with previous findings for high purity Mg.Finally, ZRA measurements indicated that the galvanic current of the Mg-3Pb alloy remained anodic for 24 hours of immersion with no polarity reversal, indicating that the Pb-containing alloy served as sacrificial anode for the AZ31, AM60, and AZ91 alloys.In conclusion, the use of Mg-3Pb alloy in cathodic protection systems for Mg alloys has proved to be a viable option in 0.1 M NaCl solution, offering new possibilities for its use in various applications.Funding: This work was supported by the State Research Agency (MICINN), the Spanish National Research Council (CSIC) and European Regional Development Fund (ERDF) under the project RYC2019-027006-I (AEI/FEDER/UE).

(Invited) A Multifunctional Polynorbonene Binder System Enabling Next-Generation Lithium-Ion Batteries

Polynobornene (PNBE), a material commonly used in your shoes or for the tires of supercars, can also be highly influential to the development of next-generation batteries (Kim et al., 2022). When designing the batteries of tomorrow, we are interested in polymeric materials with precisely defined dynamic mechanical properties, increased ionic or conductivity, specific chemical interactions and moonshots like stable and healable interfaces (Lopez et al., 2019). PNBE provides high chemical and thermal stability, low shrinkage, and strong adhesion properties that lead to enhanced electrode stability and electrical conductivity(Le et al., 2020). Possessing a highly flexible nature allows PNBE to conform to the shape of an electrode – making PNBE an ideal multifunctional binder.Consider some persisting problems associated with batteries, for example Si electrodes typically fail due to cracks in the Si particles creating new surfaces for electrolyte decomposition/solid electrolyte interphase formation, and due to the Si becoming electrically disconnected from the rest of the electrode and ultimately terminating cycling (Ryu et al., 2004) . PNBE can address both aforementioned pain points, low shrinkage and flexibility can help mitigate the impact of cracking that occurs within an electrode over time by maintaining the structural integrity, and strong adhesion properties promote effective binding of the active material and the rest of the electrode. With increasing concerns about cobalt, there has been a move to replace oxides with phosphates. Substituting a substantial fraction of Mn, for Fe in LiFePO4 leads to a material with an energy density approaching that of the oxides, while substantially lessening environmental concerns. Unfortunately, Mn dissolution causes a poor cycle lifetime.In an effort to reduce Mn dissolution, a mixture of PNBE and PVDF was used as a binder system. The PNBE was designed to have ether-type comb-branch functionalities that aid in Mn trapping, while the PVDF had suitable viscosity and mechanical properties. Figure 1 shows cycle lifetime results conducted at 45°C on a 2Ah LMFP-Graphite cell containing a 4%PVDF/1%PNBE binder system. The results show very good lifetime, with the capacity retention nearly 90% after 1,000 cycles. Given the difficulty with cycling of LMFP due to Mn dissolution, these results show good promise for this approach.This talk will highlight the opportunities and challenges of custom and enabling PNBE binder systems for LMFP, and other battery systems. References Kim, N.-Y., Moon, J., Ryou, M.-H., Kim, S.-H., Kim, J.-H., Kim, J.-M., Bang, J., & Lee, S.-Y. (2022). Amphiphilic Bottlebrush Polymeric Binders for High-Mass-Loading Cathodes in Lithium-Ion Batteries. Advanced Energy Materials, 12(1), 2102109. https://doi.org/https://doi.org/10.1002/aenm.202102109Le, D., Samart, C., Lee, J.-T., Nomura, K., Kongparakul, S., & Kiatkamjornwong, S. (2020). Norbornene-Functionalized Plant Oils for Biobased Thermoset Films and Binders of Silicon-Graphite Composite Electrodes. ACS Omega, 5(46), 29678–29687. https://doi.org/10.1021/acsomega.0c02645Lopez, J., Mackanic, D. G., Cui, Y., & Bao, Z. (2019). Designing polymers for advanced battery chemistries. Nature Reviews Materials, 4(5), 312–330. https://doi.org/10.1038/s41578-019-0103-6Ryu, J. H., Kim, J. W., Sung, Y.-E., & Oh, S. M. (2004). Failure Modes of Silicon Powder Negative Electrode in Lithium Secondary Batteries. Electrochemical and Solid-State Letters, 7(10), A306. https://doi.org/10.1149/1.1792242 Figure 1

Doped Micron Silicon and Mxene Based Composite Anodes for High-Performance Li-Ion Batteries

With the world's energy needs constantly increasing, renewable energy sources must be technologically advanced and integrated with energy storage devices to ensure their uninterrupted operation. In recent decades, researchers have devoted substantial efforts to improve the energy density of lithium-ion batteries (LIBs) [1]. While graphite remains the commercial anode in LIBs, it’s very low theoretical capacity (372 mAh g-1) restricts its use in high-energy applications. Silicon (Si), owing to its high theoretical capacity of 4200 mAh g-1, natural abundance, and appropriate Li uptake potential (0.4 V vs Li/Li+), is a promising anode material [2]. However, its massive volume expansion restricts its practical use.In this study, micron-sized Si particles are combined with graphite. Micron Si is less expensive, and the synthesis process is simpler. The well-ground mixture (Si-G) is mixed with a polymer solution to generate pyrolytic carbon (upon carbonising). This aids in the buffering of mechanical stresses caused by Si volume expansion. Furthermore, direct exposure of Si to the electrolyte is avoided, stabilising the solid electrolyte interphase (SEI). The addition of a dopant improves the intrinsic conductivity of the material, resulting in increased capacity by providing electron and Li-ion transport channels. To further enhance the composite's performance, synthesized Mxene is added to promote the charge transport between micron Si. Using various techniques such as SEM-EDAX, XRD, Raman, and XPS spectroscopy, the composite's morphology and structure is studied which reveals uniformly distributed Si, C, and Mxene sheets that retain the sheet architecture.As an anode, the composite exhibits outstanding electrochemical performance which was evident by its impressive lithium storage specific capacity of 2003 mAh g-1 (based on weight of Si) even after long term cycling (at 1C rate). Additionally, the composite demonstrates superior rate performance with a specific capacity of 2439 mAh g-1 at 10 C rate, highlighting its potential for high-power applications. Moreover, the electrode displayed a low charge transfer impedance and fast electron transport, which improved the electrochemical performance. The reason for this improved performance is the unique structure consisting of Mxene and doping, which significantly increased the Li ion diffusion and the active sites. Also, low-cost micron Si is used which has a high tap density. Thus, this work provides an approach to develop high-capacity LIBs based on silicon. Keywords: Lithium-ion battery, micron silicon anode, Mxene, doping. References Liu, L. Kang, J. Hu, E. Jung, J. Zhang, S.C. Jun, Y. Yamauchi, Unlocking the Potential of Oxygen-Deficient Copper-Doped Co 3 O 4 Nanocrystals Confined in Carbon as an Advanced Electrode for Flexible Solid-State Supercapacitors, ACS Energy Lett. 6 (2021) 3011–3019. https://doi.org/10.1021/acsenergylett.1c01373.Zhou, Y. Liu, C. Du, Y. Ren, T. Mu, P. Zuo, G. Yin, Y. Ma, X. Cheng, Y. Gao, Polyaniline-encapsulated silicon on three-dimensional carbon nanotubes foam with enhanced electrochemical performance for lithium-ion batteries, Journal of Power Sources. 381 (2018) 156–163. https://doi.org/10.1016/j.jpowsour.2018.02.009.

(Invited) Extending Cycle and Calendar Life of Si Based Li-Ion Batteries By Localized High Concentration Electrolytes

Si is one of the most promising anode materials for the next generation of lithium (Li) ion batteries (LIBs). Recently, we have developed a porous Si with a unique carbon coating structure (“carbon on Si” instead of “Si on carbon”). The nano-porosity of the materials absorbed most of volume expansion so the particles (between 3-5 mm) can retain their integrity during cycling instead of breakdown observed in bulk Si particles. Although single layer pouch cells (Si/NMC622, 62 mAh) with this porous Si anode and baseline electrolyte (1.2 M LiPF6 in EC-EMC (3:7 by wt.) +10 wt.% FEC) can retain 91% capacity after 800 cycles, their calendar life is still far shorter from 10-year target required by electrical vehicles.In this work, we present a systematic investigation of the application of localized high concentration electrolyte (LHCE) to extend the cycle life and calendar life of Si-LIBs. A typical LHCE contains a Li salt (typically LiFSI) with high solubility in a common solvent (such as DMC), and a diluent (such as TTE) with minimal solubility of the Li salt. Compared with other electrolyte design, one distinct advantage of LHCE is that solvent and diluent in LHCE can be largely decoupled from each other: change in once components will have not significantly affect the functionality of other components. This characteristic of LHCE enables much more freedom in the electrolyte designs to satisfy different practical application needs (such as long cycle life, long calendar life, high rate, high temperature, and high voltage). For example, Si/NMC622 cells with a composition of LiFSI-2.15DMC-0.17VC-0.69FEC-4.31TTE (in molar ratio) have increased cycle life of Si/NMC622 pouch cells to 2000 cycles with 80% capacity retention at 25°C as compared with 1000 cycles when baseline electrolyte was used. However, this electrolyte is less stable when LiCoO2 is used as the cathode, leading to rapid capacity loss at elevated temperatures (45°C). One possible reason for this is that cobalt in the cathode leads to more rapid decomposition of FEC than in the case of NMC622 at 45°C. On the other hand, the stability of LHCE is significantly affected by the amount of free (unbound) solvent (including DMC, VC, and FEC in the above example) in the electrolyte. By minimizing the amount of total free solvents, an electrolyte with a composition of LiFSI-2DMC-0.1EC-0.1FEC-3TTE has led to a long cycle life of Si/NMC622 cells at 25°C. Increasing the amount of main solvent in the electrolyte can further increase the conductivity of the electrolyte and significantly increase the charge/discharge rate of the cells.The long calendar life of Si-LIBs can be measured by accelerated tests at elevated temperatures (up to 55°C). Although FEC-containing electrolytes can increase the cycle life of Si-LIBs at room temperature, most Si-LIBs with FEC-containing electrolytes exhibit a rapid increase in impedance at elevated temperature, leading to a short projected-calendar-life. We designed a series of experiments to investigate the effect of FEC on the calendar life of Si-LIBs. The results clearly indicate that the formation of a high impedance interphase layer on the anode and cathode surfaces due to the decomposition of FEC at high temperatures is one of the fundamental reasons for the short calendar life of Si-LIBs. By replacing FEC with an alternative additive, a new LHCE electrolyte has been designed that led to much better cycling stability of Si-LIBs at 45°C (less than 5% capacity loss in 500 cycles) and much longer calendar life. More details of these investigations will be reported in this presentation.

Operando Investigation of Silicon Anodes During Electrochemical Cycling in Li-ion Batteries.

Silicon (Si) is recognized as a promising anode material for next-generation anodes due to its high capacity. However, large volume expansion and active particle pulverization during cycling rapidly deteriorate the battery performance. The relationship between Si anode particle size and particle pulverization, and the structure evolution of Si particles during cycling is not well understood. In this study, a quantitative, time-resolved "operando" small angle X-ray scattering (SAXS) investigation into the morphological change of unwrapped and reduced graphene oxide (rGO) wrapped Si nanoparticles (Si@rGO) is conducted with respect to the operating voltage. The results provide a clear picture of Si particle size change and the role of nonrigid rGO in mitigating Si volume expansion and pulverization. Further, this study demonstrates the advantage of "operando" SAXS in electrochemical environments as compared to other approaches.

Production of spherical Mo and Mo-Si powders by spray drying of Si suspension in a water-soluble Mo precursor

The study focuses on the production of molybdenum (Mo) and molybdenum-silicon (Mo-Si) powders using the spray drying method, followed by calcination and reduction steps. Mo powder was produced from an aqueous solution of ammonium hexamolybdate (AHM), while composite Mo-Si powders were produced from the same solution with suspended submicrometric Si particles. The as-sprayed powders were amorphous and had spherical hollow-shell morphology. In the case of Mo-Si composite powders, the powders had uniformly embedded Si aggregates on the surface. The spherical hollow-shell morphology of the powders was retained after calcination and reduction treatments. The observed chemical transition was AHM → MoO3 → Mo for Mo powders and AHM-Si → MoO3-Si → Mo-Si for composite powders. Extrusion tests demonstrated the suitability of the produced powders for extrusion-based additive manufacturing. The powders were extrudable at low load, resulting in stable filaments that stack layer by layer without deformation. The extruded filaments were then subjected to debinding and sintering processes, reaching an intermediate state of densification. Filaments fabricated from composite Mo-Si powders confirmed the alloying of Mo grains with Si during the sintering process.

Tailoring Three-Dimensional Cross-Linked Networks Based on Water-Soluble Polymeric Materials for Stable Silicon Anode.

For stable battery operation of silicon (Si)-based anodes, utilizing cross-linked three-dimensional (3D) network binders has emerged as an effective strategy to mitigate significant volume fluctuations of Si particles. In the design of cross-linked network binders, careful selection of appropriate cross-linking agents is crucial to maintaining a balance between the robustness and functionality of the network. Herein, we strategically design and optimize a 3D cross-linked network binder through a comprehensive analysis of cross-linking agents. The proposed network is composed of poly(vinyl alcohol) grafted poly(acrylic acid) (PVA-g-PAA, PVgA) and aromatic diamines. PVgA is chosen as the polymer backbone owing to its high flexibility and facile synthesis using an ecofriendly water solvent. Subsequently, an aromatic diamine is employed as a cross-linker to construct a robust amide network that features a resonance-stabilized high modulus and enhanced adhesion. Comparative investigations of three cross-linkers, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-oxidianiline, and 4,4'-oxybis[3-(trifluoromethyl)aniline] (TFODA), highlight the roles of the trifluoromethyl group (-CF3) and the ether linkage. Consequently, PVgA cross-linked with TFODA (PVgA-TFODA), featuring both -CF3 and -O-, establishes a well-balanced 3D network characterized by heightened elasticity and improved binding forces. The optimized Si and SiOx/graphite composite electrodes with the PVgA-TFODA binder demonstrate impressive structural stability and stable cycling. This study offers a novel perspective on designing cross-linked network binders, showcasing the benefits of a multidimensional approach considering chemical and physical interactions.

Boosting the grain refinement of commercial Al alloys by compound addition of Sc

For decades, Al–Ti–B has been widely used for refining commercial Al alloys. However, the addition of Al–Ti–B master alloys to recycled Al alloys suffers from Si-poisoning and cannot achieve desired refinement and thus final strength-ductility. In this study, a novel grain refiner made of Al–Ti–B-Sc has been developed and its application in refining recycled Al–Si–Cu alloys has been quantified using X-ray computed tomography (XCT). It has been found that the new Al–5Ti–1B-0.8Sc master alloy exceed the performance of Al–5Ti–1B in three aspects: (1) formation of Al3(Sc,Ti) heterogeneous nucleation particles other than Al3Ti; (2) dispersing TiB2 by forming TiB2/Al3(Sc,Ti) clusters and increasing Al melt viscosity; (3) reducing the specific surface area of Al3Ti to improve its high-temperature stability. Surprisingly, the compound addition of Sc has been found to further reduce the grain and Si particle size due to accelerated kinetics of α-Al nucleation and diminished Si poisoning. Therefore, this study proposes not only a new master alloy but also a new grain refinement method, which can effectively increase the tensile strength and elongation of recycled Al alloys up to 433.2 ± 10.5 MPa and 3.0 ± 0.1 %, respectively.

Stimulating adequate strengthening effect through alloying regulation for powder metallurgy CNTs reinforced aluminum matrix composites

Carbon nanotubes (CNTs) reinforced aluminum matrix composites (AMCs) have light weight and high specific strength, showing great potentials for making key structural components in aerospace and transportation industries. Aiming to address the bottleneck problem of unsatisfactory strengthening effect caused by the weak intrinsic interface and adverse interface reaction between CNTs and Al matrix, Si alloying element was added into Al-CNTs system via powder metallurgy method in this study. It was found that the introduction of Si element led to an inhibitory effect on Al-CNTs interface reaction. The discontinuous Al/Si/CNTs composite interface formed by the precipitation of Si significantly improved the wettability of Al/CNTs interface and enhanced its interface bonding through the pinning effect of Si particles, effectively promoting the full play of the load-bearing effect of CNTs. Furthermore, Si particles were effectively refined and passivated through appropriate heat treatment, which facilitated its dispersion strengthening and dislocation strengthening effect, and significantly reduced cracks of coarse Si particles. As a result, the synergistic strengthening effect of CNTs and micro-nano Si particles was significantly exerted in AMCs, remarkably improving the performance of Al–Si-CNTs composites.

INFLUENCE OF NICKEL ON THE MICROSTRUCTURAL EVOLUTION AND MECHANICAL PROPERTIES OF LM6-ALLOY-BASED FUNCTIONALLY GRADED COMPOSITE TUBES

Despite the growing demand for new materials, we used the horizontal centrifugal casting technique to synthesize functionally graded composite (FGC) tubes using an LM6 alloy containing (3, 6 and 9) w/% nickel. All the fabricated tubes were evaluated for variations in microstructure, hardness and tensile properties along the radial cross-section in three distinct zones (inner, transition and outer). X-Ray diffraction (XRD) results indicated the formation of in-situ Al3Ni in all FGC tubes, and these in-situ tri-aluminides increased further with the addition of Ni. A comprehensive microstructural analysis across the tubes utilising scanning electron microscopy (SEM) images showed that gathering in-situ Al3Ni particles keeps growing nearer the outer zone, and primary Si cuboids increase in the inner zone. This accumulation of particles improved the mechanical properties at all three zones of the FGC tubes compared to the LM6 tube having no nickel. The results of the hardness investigation showed that precipitated Al3Ni in FGCs has a beneficial impact on the enhancement of hardness. Furthermore, the observed UTS improvement in the FGC tubes was clearly associated with the precipitation and strengthening action of Al3Ni intermetallic phases, while a significant reduction in elongation has been noted. Due to the influence of centrifugal force and density variation, the tube containing 9 w/% of Ni demonstrated good gradation among composite alloy-fabricated FGC tubes, with in-situ Al3Ni particles settling largely in the outer zone and primary Si particles settling primarily in the inner zone across the radial thickness.

Nano-Si for On-Demand H2 Production: Optimization of Yield and Real-Time Visualization of Si─H2O Reaction Using Liquid-Phase Transmission Electron Microscopy.

Hydrogen (H2), the most abundant element in the universe, has the potential to address the challenges of energy security and climate change. However, due to the lack of a safe and efficient method for storing and delivering hydrogen, its practical application is still in its infancy stages. To overcome this challenge, a promising solution is demonstrated in the form of on-demand production of H2 using nano-Silicon (Si) powders. The method offers instantaneous production of H2, yielding a volume of 1.3 L per gram of Si at room temperature. Moreover, the H2 production yield and the rate can be effectively controlled by adjusting the reaction pH value and temperatures. Additionally, liquid-phase transmission electron microscopy (LPTEM) is utilized in situ to demonstrate the entire reaction in real-time, wherein H2 bubble formation is observed and illustrated the gradual conversion of crystalline Si particles into amorphous oxides. Moreover, it is confirmed that the purity of the generated gas is 99.5% using gas chromatography mass spectrometry (GC-MS). These findings suggest a viable option for instant H2 production in portable fuel cells using Si cartridges or pellets.

Facile Synthesis of 2D SiOx-3D Si Hybrid Anode Materials by Ca Modification Effect for Enhanced Lithium Storage Performance.

Al-Si dealloying method is widely used to prepare Si anode for alleviating the issues caused by a drastic volume change of Si-based anode. However, this method suffers from the problems of low Si powder yield (<20wt.% Si) and complicated cooling equipment due to the hindrance of large-size primary Si particles. Here, a new modification strategy to convert primary Si to 2D SiOx nanosheets by introducing a Ca modifier into Al-Si alloy melt is presented. The thermodynamics calculation shows that the primary Si is preferentially converted to CaAl2Si2 intermetallic compound in Al-Si-Ca alloy system. After the dealloying process, the CaAl2Si2 is further converted to 2D SiOx nanosheets, and eutectic Si is converted to 3D Si, thus obtaining the 2D SiOx-3D Si hybrid Si-based materials (HSiBM). Benefiting from the modification effect, the HSiBM anode shows a significantly improved electrochemical performance, which delivers a capacity retention of over 90% after 100 cycles and keeps 98.94% capacity after the rate test. This work exhibits an innovative approach to produce stable Si-based anode through Al-Si dealloying method with a high Si yield and without complicated rapid cooling techniques, which has a certain significance for the scalable production of Si-based anodes.

Insight into the fracture behaviour and mechanical response of ECAP processed cast and LPBF AlSi10Mg alloy

This paper presents a comparative analysis of the microstructure, tensile deformation and fracture mechanisms of an ECAP-processed AlSi10Mg alloy produced by two different methods: selective laser melting (SLM) and casting. The evolution of the microstructure was investigated using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In addition, internal structural defects were analysed using X-ray computed tomography scans (CT). To investigate the mechanical properties and crack propagation during tensile deformation, a real-time visualization through in-situ tensile CT scans, along with the loading–unloading-reloading tensile test (LUR) was employed. The results showed significant differences in the mechanical property between the two ECAP-processed samples. Specifically, the SLM sample exhibited an approximately 50 % higher tensile strength of 370 MPa and a remarkable elongation at break of 12 %. Detailed microstructural analysis showed that the additional work hardening occurred mainly in the hetero-zones, where the accumulation of geometrically necessary dislocations developed back and forward stresses, which together led to the hetero-deformation induced (HDI) stresses. Further quantification of the (HDI) stress derived from the loading–unloading-reloading tensile test (LUR) confirmed origin of the additional strain hardening in the SLM specimen. Fractographic analysis showed that the poor tensile ductility of the ECAP-processed cast specimen was primarily due to the low bonding between Al and Si particles, resulting in premature fracture. In contrast, the ECAP-processed SLM specimen fractured predominantly along the softer heat-affected zones (HAZ).